The present invention relates to an optical information (or data) recording/reproducing apparatus which is capable of confirming the recorded signal immediately after the signal has been recorded.
When a signal is to be recorded on a recording medium in a magnetooptical data recording/reproducing apparatus which is one species of the optical information recording/reproducing apparatus, a magnetic field is applied to a recording film of the recording medium while the recording film is illuminated with a laser beam for rising the temperature thereof (this laser beam will hereinafter be referred to as writing or heating laser). Because of the rise in temperature of the film, the coercive force of the recording film is lowered. As the result, when the coercive force of the recording film becomes lower than the intensity of the magnetic field applied to the film, the corresponding portion thereof is magnetized in the direction of the applied magnetic field. It is thus possible to record on the recording film a signal consisting of a bit-based pattern containing a train of bits "1" and "0" by magnetizing previously the recording film in a predetermined direction and applying the magnetic field to the recording film in the direction opposite to that of the magnetization while the intensity of the laser beam is modulated with the signal consisting of the bit pattern mentioned above. Alternatively, the direction of the applied magnetic field may be reversed for each of the bits "1" and "0" with the intensity of the laser beam being maintained constant.
In the first mentioned recording method, the preparatory uniform magnetization of the recording film in the predetermined direction is performed for the purpose of erasing the signal recorded previously in precedence to the recording of new signal. Without the preprocessing for the erasure of signal, the signal recorded previously will continue to remain in the region in which the new signal is to be recorded. In other words, the means for erasing precedently the old signal recorded previously is necessary because of the impossibility of recording the new signal in superposition to the old signal in the case of this method. In contrast, in the case of the second mentioned recording method according to which the direction of the applied magnetic field is reversed in accordance with the bit "1" or "0" of the signal to be recorded, the recording film is always magnetized in the direction of the applied magnetic field, which means that the preparatory erasure of the old signal recorded is unnecessary, allowing thus the recording in overlap.
An example of the apparatus in which the second mentioned recording method is used is disclosed in Japanese Patent Publication No. 48806/1985 (JP-A-60-48806). This known apparatus in which a single laser source is employed is implemented so as to be also capable of reproducing the recorded signal. More specifically, in the signal reproduction mode, a recording film of the recording medium having signal recorded thereon is illuminated with a laser beam emitted from a laser source, wherein the laser beam undergoes the Kerr effect due to the magnetization of the recording film. As the consequence, the laser beam reflected by the recording film exhibits different directions of rotation of the plane of polarization in dependence on the directions of magnetization of the recording film. Accordingly, by detecting discriminatively the directions of rotation of the plane of polarization of the reflected laser beam, an electric signal consisting of a bit pattern such as mentioned above can be derived.
Parenthetically, in order to enhance the reliability of the recording medium, it is necessary to confirm whether or not the signal of interest has correctly been recorded on the recording medium every time the signal recording is performed. This confirmation can be accomplished by actually reproducing the signal from the recording medium. However, when the single laser beam is employed both for the signal reproduction from the recording film and for rising the temperature thereof for the purpose mentioned above, as in the case of this known recording/reproducing apparatus, the confirmation of the recording by reproducing the signal is possible only after the power of laser beam is set in succession to the completed recording of the signal of interest to such a level at which the coercive force of the recording film cannot be weakened. In particular, in the case where the recording medium is in the form of a disk, the signal reproduction for the confirmation must be performed after a complete rotation of the recording disk in succession to the recording of the signal of concern. Thus, a great amount of time unavoidably intervenes between the start of the signal recording and completion of the confirmation for the correct recording of the signal. This in turn means that the signal recording process involves a great deal of time.
On the other hand, there is disclosed in Japanese Patent Application Laid-Open No. 162137/1972 (JP-A-57-162137) an optical recording/reproducing apparatus in which two laser beams are employed, wherein one of the laser beams is used for rising the temperature of the recording film (i.e. the writing or heating laser beam) with the other laser beam being used for the reproduction of the signal (this laser beam will hereinafter be referred to as the reading beam). With this known technique, it is possible to effectuate the confirmation of the recorded signal substantially simultaneously with the recording of signal by illuminating the region of the recording film with the reading laser beam immediately following the recording of the signal. A magnetooptical recording/reproducing apparatus which is implemented on the basis of the concept disclosed in the patent application cited just above is shown in FIG. 1 of the accompanying drawings. Discussion on this apparatus will be made below. In FIG. 1, reference numeral 1 denotes a recording medium, 2 denotes a focussing lens, 3 denotes a mirror, 4 denotes a beam splitter, 5 denotes a polarizer, 6 denotes a collimator, 7 denotes a laser source for rising temperature of a recording film, 8 denotes a laser source for signal reproduction, 9 and 9' denote lenses, 10 and 10' denotes detectors, 11 denotes a magnetic field modulating coil, 12 denotes a semitransparent mirror, 13 denotes an analyzer, 14 and 14' denote laser drive circuits, 15 and 15' denote amplifiers, 16 denotes a low-pass filter (LPF), 17 and 17' denote input terminals, 18 denotes a wavelength separation filter, and 19 and 19' denote output terminals.
In operation in the recording mode, predetermined voltages are applied to the input terminals 17' and 17 for activating the laser drive circuits 14' and 14, respectively, to thereby drive continuously the heating or writing laser source 7 and the reproducing or reading laser source 8. Laser light of high power emitted from the heating laser source 7 is reflected by the semi-transparent mirror 12 and subsequently collimated by the collimator 6 to a laser beam to be used for rising the temperature of the recording film (i.e. for heating the recording film). The heating or writing laser beam is then polarized by the polarizer 5 to be subsequently focussed onto the recording film of a moving recording medium through the focussing lens 2 after having passed through the beam splitter 4 and having been reflected by the mirror 3. As the result, a minute portion of the recording film is heated to a high temperature. On the other hand, the magnetic field modulating coil is supplied with a signal current with the polarity inverted in dependence on the signal bit "1", "0", as the result of which the magnetic field of the direction reversed in dependence on the signal bit "1", "0" is generated by the magnetic field modulating coil 11 and applied to the heated portion of the recording film on the recording medium 1. Thus, under the effect of the heating and the applied magnetic field, the signal is magnetically recorded on the recording film of the recording medium.
The reading laser source 8 for the signal reproduction emits laser light of low power, which is passed through the semi-transparent mirror 12 to be subsequently collimated by the collimator 6 to a reading laser beam for the signal reproduction. This reading laser beam is then focussed by the focussing lens 2 onto the recording film of the medium 1 at a position located on the recording film immediately behind the portion illuminated by the writing laser beam (as viewed in the moving direction of the recording medium) after having been transmitted along the optical path defined by the polarizer 5, beam splitter 4 and the mirror 3. In this case, the power of the reading laser beam for the signal reproduction is set at a low level at which the recording film on the recording medium 1 is protected from being heated to such a high temperature which brings about the inversion of magnetization.
FIG. 2 shows another example of the magnetooptical recording/reproducing apparatus of the magnetic field modulation type, which differs from the apparatus shown in FIG. 1 in that a quarter-wavelength plate 30, a polarized beam splitter 31 and a second detector 10-2 are additionally provided.
In operation, the recording film of the recording medium reflects a part of the writing laser beam and the reading laser beam. At that time, since the reading laser beam illuminates the portion of the recording film in which the signal is recorded, the reading laser beam undergoes the Kerr effect due to the magnetization of that portion. More specifically, the plane of polarization of the reflected reading laser beam is rotated relative to the incident beam illuminating the recording film. In that case, the direction of the rotation differs in dependence on the direction of magnetization of the recording film.
The reading laser beam reflected by the recording film on the recording medium 1 reaches the wavelength separating filters 18-1 and 18-2 by way of the focussing lens 2 and the mirror 3. The optical path defined by the collimator 6, beam splitter 4, mirror 3 and the focussing lens 2 is utilized in common to both the writing laser beam and the reading laser beam. Further, a part of the writing laser beam partially reflected by the recording film of the recording medium 1 follows the same optical path as the reflected reading laser beam. The reflected reading laser beam is utilized for confirming the recorded signal. Accordingly, the reflected reading laser beam has to be separated from the reflected writing (heating) laser beam. To this end, it is required that the wavelength of the writing (heating) laser beam differs from that of the reading laser beam. Thus, there are employed the wavelength separating filters 18-1 and 18-2. By way of example, the writing laser beam may have the wavelength of 830 nm while that of the reading laser may be 780 nm.
The optical separation filter 18-2 allows the reading laser beam to pass therethrough while reflecting the writing laser beam. The reading laser beam having passed through the optical separation filter 18-2 is separated into two orthogonal polarized light components by the polarizing beam splitter 31-2 through the lens 9-2 to be subsequently received by the detectors 10-2 and 10-3.
Thus, the detectors 10-2 and 10-3 outputs electric signals of such level which varies in dependence of the directions of magnetization of the recording film on the recording medium 1 (i.e. in dependence on the recorded signal "1" and "0"). These signals reproduced from the recording medium 1 are differentially amplified by the amplifier 15-2 and applied to the LPF 16 where noise components are eliminated. The output signal of the LPF 16 is taken out through the output terminal 19 to be utilized for confirming the recorded signal.
On the other hand, the writing laser beam reflected by the optical separation filter 18-2 is received by the detector 10-1 by way of the beam splitter 4 and the lens 9-1. The detection output signal of the detector 10-1 is amplified by the amplifier 15-1 and outputted through the output terminal 23 to be utilized in monitoring the power of the writing laser beam or as the tracking and focussing control signal.
In addition to the magnetooptical recording/reproducing apparatuses described above, the present invention concerns a write-once type recording/reproducing apparatus which is another species of the optical information recording/reproducing apparatus and in which a write-once type optical recording medium is employed instead of the magnetic recording medium.
The signal recording on the write-once type optical recording medium is accomplished by making use of the phenomenon that a recording film of this type recording medium absorbs energy of the illuminating laser beam to convert it into heat by which a spot region of the recording film illuminated with the laser beam is bored or otherwise deformed through melting, sublimation, decomposition, vaporization and the like process, whereby the information signal consisting of a bit pattern of "1" and "0" is recorded in the recording film in the form of pits. When the pit information as recorded is to be read out or reproduced, the recording film is illuminated with a reading laser spot of power sufficiently low for precluding the thermal influence to the film, wherein the recorded information is read out by detecting discriminatively the light reflection of low level originating in the pit and the reflection of high level from other region than the pit.
FIG. 3 of the accompanying drawings shows a write-once type optical recording/reproducing apparatus, which differs from the magnetooptical recording/reproducing apparatus shown in FIG. 1 in that the magnetic head 11, polarizer 5, the analyzer 13 and other associated parts are absent.
FIG. 4 shows another example of the write-once type recording/reproducing apparatus in which a write-once type optical disk is employed as the recording medium and which is implemented in the structure similar to the apparatus shown in FIG. 3 except that a control circuit for performing a tracking control on the basis of error signal involved in the tracking/focussing operation is incorporated.
As will be seen from the foregoing description, there are the optical information recording/reproducing apparatuses which are capable of confirming the signal recording simultaneously as the signal is recorded.
It is however noted that in the optical information recording/reproducing apparatus, an optical system is used in common to both the writing laser beam and the reading laser beam which differ from each other in the wavelength. Consequently, correction of aberrations is required for each of the laser beams. Besides, a filter is necessary for separating these two laser beams from each other. Under the circumstances, the optical system necessarily presents a complicated structure, making difficult the assembling and adjustment, not to speak of poor utilization efficiency of the laser beam because of presence of many parts absorbing the laser energy.